Inkjet printers are widely used not only as output means for personal computers, but also as means for printing on media of various materials. Widely used as inks for inkjet printers now are those composed of organic dyes dissolved in water or other solvents, and organic dyes include azo dyes, anthraquinone dyes, indigo dyes, phthalocyanine dyes, carbonium ion dyes, nitro dyes, quinoline dyes, naphthoquinone dyes, etc.
To clearly develop the color of the above inks while preventing the printed ink from blurring, so-called coated papers comprising ink-bearing layers made of high-water-absorption resins on surface, as disclosed by Japanese Patent Laid-Open Nos. 59-35977 and 1-135682, are used for inkjet printers. Such coated papers, however, are high in production cost because of special coatings, and lack in such hand as that of plain papers. Accordingly, demand is now mounting on commonly usable, inexpensive plain papers suitable for inkjet printers.
When a plain paper is used for an inkjet printer, however, the ink diffuses along fibers of the paper in the course of absorption into the paper, resulting in ink dots with excess blur, irregular peripheries, indistinct outlines, feathering, etc. Thus, clear letters and image cannot easily be obtained, causing the problem that image produced by an inkjet printer is insufficient in water resistance.
Against such a problem, Japanese Patent Laid-Open No. 10-119425 proposes a plain paper for inkjet printing, coated with a coating composition liquid comprising as effective components a cationic polymer and a water-soluble resin, the cationic polymer being a polymer consisting essentially of a quaternary ammonium salt of alkyl (meth)acrylamide having a benzyl group. However, the inkjet printing paper of Japanese Patent Laid-Open No. 10-119425 is insufficient in clarity of image and color development of ink when full-color inkjet printing is conducted. Therefore, further improvement of inkjet printing quality is desired.